1. Field of the Invention
The invention relates to a control device and a control method of an exhaust purification device.
2. Description of the Related Art
Some diesel engines and the like have, in their exhaust passageways, an exhaust purification device that includes a catalyst for purifying the exhaust gas. Examples of such catalysts include a NOx storage-reduction catalyst, which remove NOx (oxides of nitrogen) by the reduction thereof, and the like. The NOx storage-reduction catalyst stores NOx from the exhaust gas in an oxidizing atmosphere, and releases stored NOx and reduces it to nitrogen in a reducing atmosphere. Specifically, when a predetermined condition regarding the engine operation state or the like is met, fuel in the fuel tank is pressure-fed, by a supply pump, through a supply passageway to an addition valve that is provided upstream of the installed position of the catalyst, and the fuel is supplied from the addition valve into the exhaust passageway (Japanese Patent Application Publication No. JP-A-6-50134).
In engines having two systems of exhaust passageways, for example, a V-type engine, each exhaust system is provided with exhaust purification devices 20R, 20L as shown in FIG. 1. Therefore, it is necessary to dispose addition valves 22R, 22L for supplying fuel to the exhaust purification devices 20R, 20L, respectively. However, because two addition valves 22R, 22L are used, the amount of fuel supplied is greater than in the case where fuel is added using a single addition valve. This greatly reduces the fuel supplying pressure. As a result, the degree of atomization of fuel in exhaust passageways 2R, 2L may deteriorate, so that the fuel may not be sufficiently supplied to the surface of the catalyst, and therefore the exhaust purification rate may drop.
The foregoing problem is not limited to the exhaust pipes into which a reductant, such as fuel or the like, is supplied, but also is generally shared by exhaust pipes into which an additive other than fuel is supplied.